Occlusion of the lines carrying fluid into the inlet of a pump or out its discharge port is normally readily evident--fluid delivery from the pump ceases or at least, is reduced. Of course, the cessation of fluid flow from a pump discharge line can also be caused by other faults, such as a failure of the pump or interruption of its power supply. In certain applications, it may be important to determine whether an occlusion of the inlet or outlet line interrupted the fluid flow, so that appropriate steps can be taken to correct the problem.
Maintenance of fluid flow from a pump may be critical, particularly in the field of medical technology in which pumps are often employed in procedures performed upon a patient. For example, interruption of the intravenous infusion of drugs into a patient's vascular system using a peristaltic, cassette, or other type of pump can have serious consequences that may endanger the patient's health. It is therefore very important that medical personnel be quickly alerted if such an interruption occurs. More importantly, to ensure that the appropriate corrective response is taken, the cause of the interruption in fluid flow should be identified. If an occlusion of the inlet (proximal) line connecting the source of the medicinal fluid to the pump inlet occurs, the monitoring system should identify that cause of the interruption; similarly, any occlusion of the outlet (distal) line connecting the pump discharge port to the patient should also be specifically identified.
One way to detect an occlusion of a proximal or distal fluid line is to monitor fluid flow in the line. Most devices for monitoring fluid flow must be installed in the line so that the fluid mechanically interacts with a flow sensor as the fluid moves through the device. However, in the case of peristaltic pumps and other types of pumps that are intended to pump fluid through an integral tube set, it is undesirable to install such flow sensors, since the installation requires cutting into the tube set on both the proximal and distal sides of the pump to insert flow in-line sensors. Instead, it is preferable to detect any occlusion of either the proximal or distal lines with a device that is installed on an integral tube set, much like a peristaltic pump. Even more preferable is an occlusion detector that is incorporated into the pump so that it does not require separate installation on the proximal and/or distal lines.
Another problem with using a conventional flow detector to determine when an occlusion has occurred is that the restriction of the line may be only partial, allowing fluid flow to continue at a reduced rate that is insufficient to trigger an alarm. If a patient rolls over onto the distal line, pinching the IV line partially closed, fluid flow through the line may be only reduced, yet the patient does not receive the prescribed dosage of the medication. The reduced flow rate caused by the restriction of the distal line may severely limit the total dose delivered during a predefined interval.
If the flow of a medicinal fluid to a patient is sufficiently reduced by a pinched distal line, pressure upstream of the flow can build so that if the occlusion of the delivery line is then removed, a potentially dangerous bolus of medicinal fluid is delivered to the patient. Accordingly, an occlusion detector should be responsive to pressure in the distal line.
Equally important in the detection of such an occlusion is avoidance of false alarms. A momentary interruption of fluid flow should not trigger an occlusion alarm, since the short term interruption of fluid flow probably has no serious detrimental consequences. Similarly, variations in the environmental conditions that might affect the detection of an occlusion should be ignored or filtered out to avoid false alarms. If the occlusion detector produces false alarms, the alarms will eventually be ignored, potentially causing a serious reduction in fluid flow to remain uncorrected.
It will therefore be apparent that a device and a method are required for detecting an occlusion of either a distal or proximal line of a pump and particularly, an occlusion of the distal or proximal line of an IV pump used to administer medical fluid to a patient. The advantages of the present invention in this regard will be apparent from the attached drawings and from the Description of the Preferred Embodiments of the Invention that follows.